In recent years, blood vessels existing inward of a living body is aimed for one of the objects of biometrics authentication.
Deoxygenetated hemoglobin (venous blood) or oxygeneted hemoglobin (arterial blood) flowing in a blood vessel has a property that uniquely absorbs lights in a near infrared band (near infrared lights). An imaging apparatus for picking up the image of blood vessels by using this property has been proposed.
Concretely, an imaging apparatus in which near infrared lights are emitted to a finger being placed on an imaging opening from a light source of near infrared light, the lights are reflected or dispersed inward of this finger, and near infrared lights entered in a housing passed through the above finger and the imaging opening are induced on the imaging plane of an image pickup device via an optical lens, so that blood vessels are imaged has been proposed (see Japanese Patent Laid-Open No. 2004-195792 (see FIGS. 2 and 15, for example.)
By the way, in an imaging apparatus having the above configuration, distortion of aberration in an optical system caused by that the distance between the finger and the image pickup device is short is corrected by a macro lens and signal processing. However, there is a limit in the reproducibility. Thus, there is a problem that improvement in image quality above a certain degree cannot be expected. More particularly, if considering that the images of blood vessels will be used as objects to be authenticated or a part of data in medical diagnosis, the problem of image quality is further serious.
On the other hand, if it is tried to physically keep the distance between the imaging opening and the object to be imaged, the thickness of the overall imaging apparatus increases for that. It is not agree with a demand for miniaturization in recent years. More particularly, it is not adequate in the case of installing the above imaging apparatus in a portable terminal device such as a cellular phone in that a demand for reduction in thickness is strong.